In the ecologically-minded city of Futo (Wind Capital), there are many windmills and the people live in harmony. However, the Sonozaki family sell mysterious USB memory sticks called Gai Memories to criminals who use them to become monsters called Dopants, committing crimes, with the police force powerless to stop them. The hardboiled (or rather half-boiled) detective Shotaro Hidari works with the mysterious Phillip who possesses the true Gaia Memory. Using their own Gaia Memory, Shotaro and Phillip use the Double Driver belts to transform and combine into Kamen Rider Double to fight the Dopant menace.